In conventional hob cutters for cutting involute gears having chamfered tooth profiles, the pressure angle exhibited by the rack of teeth on the hob, the "hob tooth profile," is the same as the nominal pressure angle of the gear to be formed. It is also known to reduce the pressure angle on the hob tooth profile to "preshave" the gear tooth profile. In both cases, the relation between the number of teeth on the gear to be cut and the appropriate chamfering value varies monotonously and continuously, such that the rate of such variation is relatively large where the number of teeth is relatively small.
In other words, prior hob cutters have been designed to optimally cut a gear having a particular number of teeth. If a gear having more than this particular number of teeth is cut, the chamfer will be increased. On the other hand, if a gear having fewer teeth than this particular number is cut with the same hob cutter, the chamfer will decrease or disappear.
Accordingly, in the prior art, one of several different hob cutters was selected responsive to the number of teeth on the gear to be cut, in order to appropriately chamfer the teeth of the gear.